Almansoura university
Faculty of Engineering
Dept. of Electronics & Electrical Commu.
Electronics 1
Final-Term Exam
Time allowed: 3 Hours
Answer the following questions; assuming any missing data.
l) a- Discuss the applications of the Darlington pair.
b- Write an expression for the input impedance of the common
collector amplifier as a function of the impedances connected to
the emitter terminal.
2) For the emitter follower (Common collector) in Fig. l, the signal
source is directly coupled to the transistor base. Find the de emitter
current. Assume fJ = 100. Neglecting ro, find Rin, the voltage gain
vJv sig- the current gain io/ii and the output resistance Rout.
3) The amplifier shown in Fig. 2 has Rsig = RL = 1 kQ, Rc = 1 ill, RB
=47 ill, ~= 100, Cu = 0.8 pF, and fT= 600 MHz.
(a) Find the de collector current of the transistor.
(b) Find gmand r1[.
(c) Neglecting r., find the midband voltage gain from base to
collector (neglect the effect of Rs).
(d) Use the gain obtained in (c) and the Miller theorem to find the
component of Rj, that arises as a result of Rg. Hence find Rin.
(e) Find the overall gain at midband.
(f) Find c..
(g) Find fH.
4) Use the circuit of Fig. 3 to design a common gate amplifier. Find Rin,
ROUb Avo, Av,
and Gi for RL =15 kQ and Rsig = 50 Q. What will the
overall voltage gain become for R sig= 50 Q? 10 kQ? 100 kQ?
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5) The circuit shown in Fig. 4 consists of two stages:
Stage 1: CE amplifier with Vcc = 12 V, Rc = 1.0 kQ and re=5Q.
Stage 2: Darlington emitter follower amplifier with voltage
divider bias, given RI = 10 kQ, R2 = 22 kQ, RE = 22 Q, RL = 8
Q, Vcc = 12 V and ~I= ~2 = 100.
a)
b)
c)
d)
Determine the voltage gain of the common-emitter amplifier.
Determine the voltage gain of the Darlington emitter-follower.
Determine the overall voltage gain.
If the circuit is without the Darlington pair, find the gain and
compare with that obtained in C.
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